Winthrop k



W. K. HOWE.

AUTOMATIC TRAIN CONTROL SYSTEM.

APPLICATION FILED DEC-4, 19l5. RENEWED MAR. 27. 1919.

Patented Nov. 30, 1920.

' IIVVE/VTOR By W fiT R/VEY UNITED STATES PATENT OFFICE- WINTHROP K. HOWE, OF ROCHESTER, NEW YORK, ASSIGNOR TO GENERAL RAILWAY SIGNAL COMPANY, OF GATES, NEJV YORK, CORPORATION OF NEW YORK.

AUTOMATIC TRAIN-CONTROL SYSTEM.

Specification of Letters Patent.

Patented Nov. 30, 1920.

Application filed December 4, 1915, Serial No. 65,070. Renewed March 27, 1919. Serial No. 285,636.

To all'whom it may concern:

Be it known that I, lVIN'rHRor K. HOWE, a citizen of the United States, and a resident of the city of Rochester, in the county of Monroe and State of New York, have invented a new and usefulAutomatic Train- Control System, of which the following is a specification. v

This invention relates to automatic train control systems, and more particularly to such systems in which the movement of the train is controlled, in some way, by the energization and deiinergization of a control relay carried on the train and governed by the contactof a contact shoe carried by the train with contact rails or ramps fixed along the trackway, said ramps being energized or (lei-Energized according to traffic condi' tions.

One of the principal objects of this invention is to devise a system for automatically controlling railway trains by the cooperation of contact shoes and contact rails which will permit the use in the same train of a number of motor cars or locomotives each equipped with the automatic train control apparatus and which will allow the simultaneous operation of the control apparatus on all of said motor cars or locomotives, regardless of the number of these motor cars or locomotives, or of their position in the train, or of the length of the blocks or the length of the train.

A further object or" the invention is to devise a system for automatically controlling railway trains by the cooperation of contact shoes and contact rails which will pre vent an excessive or dangerous flow of current in cases where the train consists of two or more motor cars or locomotives each equipped with the train control apparatus and connected together electrically by a continuous conductor so as to operate simultaneously, and where the train passes over a block which is shorter than the length of said train.

Other objects and advantages will appear as the description of the invention progresses, and the novel features of the invention will be particularly pointed out in the appended claims. Y

enerally stated, the invention consists 1n arranging a suitable current limiting device so that it can be placed in the controlllng circuit for each ramp along which the improper or excessive current would flow, and in providing suitable means for placing said current limiting device in said controlling circuit whenever said improper current commen-cos to flow.

The invention further consists in the parts, and in the arrangements and combinations of parts and of the controlling circuits therefor, which will be more fully set forth hereinafter.

In describing the invention in detail, reference is had to the accompanying drawing', wherein I have illustrated a preferred physical embodiment of my invention, and wherein like characters of reference designate corresponding parts throughout the several views, and in which:

The figure is a diagrammatic view of a train, and the track therefor, and shows the trackway is divided into electrically distinct sections A, B, C, and D by means of suitable isulating joints 3. These blocks may be of any suitable length required to obtain the desired spacing of the trains. At the entrance to each block a ramp or contact rail 1 R is supported in any suitable manner along the trackway, as for example, adjacent to the track rail 2, and so as to be insulated from said track rail.

The current for energizing the parts of the train control apparatus and their controlling circuits located along the trackway is derived from two main line wires 4 and 5 which are connected to a suitable sourceof current, as a generator 6. In the particular arrangement of the parts and controlling circuits illustrated in the drawing, the ener y used as the operating medium is assumed to be alternating current.

The. parts and electrical connections between said parts associated with each block and each ramp are the same, and for siniplicity and clearness these parts and electrical connections associated with the block C will be given the same reference characters as the corresponding parts of the block B, with the distinctive exponent 1 added thereto. The normal direction of traiilc is indicated by the arrow at.

Adjacent to one end of each block, preferably the exit end, is a track transformer 7, the primary of which is connected to the line wires 4 and 5, and the secondary of which is connected by wires 8 and 9 to the track rails 1 and 2, respectively. At the other end of each bloclr is located a track relay 10 which is connected by wires 11 and 12 to the track rails 1 and 2, respectively, and which is provided with two circuit controlling armatures 13 and 1a represented according to the well known convention. The track transformers 7 and the track relays 10, together with the track rails 1 and 2 of each block, constitute the well known normally closed track circuit, the operation of which will be apparent to those skilled in the art.

The current for energizing the ramps R and for controlling the parts of the train control system carried by the train is supplied from a transformer 15 located adjacent to each ramp R. transformer 15 is connected to the line wires 4 and 5, and one terminal of the secondary of said transformer 15 is connected by a conductor 16 to the electrically continuous track rail 1-, said secondary being provided with two taps 17 and 18 by means of which suitable voltages necessary for the proper operation of the system may be obtained.

In the particular physical embodiment of the invention illustrated in the drawing the current limiting device is an impedance 25 which is connected in a partial controlling circuit for each ramp, as explained more fully hereinafter. Each impedance is ar-- ranged so that it can be shunted or included in its corresponding ramp controlling cir cuit, and the shunt around the impedance 25 is opened and closed by the movement of: an armature 19 of a suitable relay or translating device S. This relay S is shown as the type known in the art as a polyphase alternating current relay and comprises two separate coils or windings which are shown in the drawing according to established convention. One coil 20 of the relay fl is connected by conductors 21 and 22 to the secondaryot a transformer 23, which has its primary connected to the line wires 4 and 5, so that the coil 20 of the relay S is energized at all times. The other coil 24- of the relay S is included in the same controlling circuit as the impedance 25. The type of the relay S shown. is well known in the art, and to obtain a clear understahdin of the nature and operation of this invention it is not deemed The primary oi each necessary to describe the construction of relay 3 in detail; and the characteristic features of this relay, in so far as they'are necessary for a clear understanding of the 'nvention, will be pointed out fully in the do, cription oi' the operation. For the purposes for which the relay S is used in this inv ntion, this relay is preferably conucted so to be quick acting, and the armature l9 and cooperating contacts controlled thereby are designed so as to be able to interrupt a comparatively large current without injury.

The conductors and the electrical connections between the diilerent operating parts of the train control system which are located along the traclrway will not be described in detail, since these electrical conductors and the different operating circuits will be fully set forth hereinafter in the description of the operation.

Referring to the parts of the train control system which are carried on the train, the train is shown diagrannnatically comprising two pairs of wheels 28-28, 2626 connected by the usual axles 29 and 2-? respectively; and these pairs of wheels and axles are connected by a bar 30 which repre sents the frame or oody of the cars or locomotives constituting the train. T119, wheels and axles illustrated are assumed to represent those in dii'ierent cars or locomotives, of which provided with suitable ti in control apparatus; and since this train control apparatus is constructed the same on each motor car or locomotive, a description cl one will suliice for all, and corresponding parts will be designated by the same refer- -e characters.

A. bracket 31 of suitable insulating inatorial is supported in any appropriate mannor On each motor car or locomotive and is shown fastened to one of the journal boxes or axles; and mounted on the bracket 31 is a vertical movable plunger or shoe which is pressed downwardly by a spring 33. The shoes 32 on the different motor cars or locomotives are arranged in the same plane as the ramps B so that, as the train passes along the track, said shoes will contact with said ramps. The shoes are designed to make electrical contactwith the ramps B, and also to be lifted in a way to actuate a suitable circuit controlling device carried on the train; and to accomplish this purpose, the shoe 32 is shown provided with an insulating button 3% arranged to lift a Contact spring 35 out of contact with a contact piece 356, when the shoe 32 is raised. The contact spring 35 and the contact piece 36 are fined to the bracket 31. and since said bracket is assumed to be of insulating material, said contact piece 36 and said contact spring 35 are electrically independent, except when the contact is closed.

being used in a system embodying this invention, it is deemed unnecessary to illustrate or describe the device K further in detail. The device K may be constructed and arranged so as to apply the brakes on the train immediately upon its operation, or

after a certain interval; or the operation of the device K may be made dependent in any suitable way upon the speed at which the train is traveling, ,or upon the speed of the train and the distance between the train and the point of danger. In the particular embodiment of the invention shown the' device K is arranged so as to be set into operation when the electrical energy which is normally supplied toit is interrupted, and the device K restored to its normal or inactive condition when electrical energy is again supplied to it. The deenergization and reenergization of the device K is controlled by an armature 39 of a control relay 37 carried on the train; and when the control relay 37 is energized, and its armature 39 is raised to its upper position, electric current is supplied to the device K from a source of current carried by the train, as a battery 40, by a circuit which may be traced as follows:

From the battery 40, conductor 41, device K, conductor 42, armature of the control relay 37 in its upper position and conductor 43 back to the battery 40.

When the shoe or plunger 32 is in its lower or normal position, the control relay 37 is supplied with current from a local source of current carried by the train, as a battery 44, by a circuit which may be traced as follows:

Circuit Number T 100.

mary of the transformer 56 is connected by a conductor 57 to the bar 30 which represents the frames of the cars constituting the train, and theother terminal ofthe primary of the transformer 56 is connected by a conductor 58 to the contact shoe 32. The terminals of the primaries ofthe transformers 56 which areconnected to the shoes 32 on the different motor cars or locomotives oi the train are connected together by a continuous conductor or bus 59.

When the alternating current pick up relay 52 is energized and its armature 53 is raised to its upper position, the control relay 37 is energized by current from the battery 44 according to a circult which may be traced as follows:

Uz'rcuz't Number Three.

1915, and for a clear understanding of the nature of the present invention, it is sufficient to explain briefly the operation of the system for a few cases of different traffic conditions. In making this explanation,

the action of the cutout relay S will be at first disregarded, the armatures 19 being assumed to be in their normal closed posi tion.

For the first traffic condition to be considered, assume that the train in question is about to enter the block B; that this train has found the traclrway unobstructed and has been able to proceed at unlimited speed without any restriction being imposed upon it by the train control device K; and that neither of the blocks B or G is occupied. Under these-conditions, the track relays 10 and 10 of the blocks B and C, respectively, are energized from the corresponding track transformers, as will be clearly understood by those skilled in the art of railway signaling. Since the track relay 10 is energized, its armature 13 is in its upper position, and and a high difference of potential exists between the ramp R and the track rail 1 ac cording to a circuit which may be traced as follows:

Orcuit Number Four.

From the ramp R, conductor 62 armature 13 of the track relay 10 in its upper position, conductor 63, high voltage tap 18 of the secondary of the transformer 15 and conductor 16 to the track rail 1.

When the first shoe 32 of the train engages the ramp R it is raised and lifts the the control relay 37 Circuit Number F'i/ve.

From the high voltage terminal or tap 18 of the secondary of the transformer 15, conductor 63, armature 13 of the track relay 110 in its upper position, conductor 62, amp R, contact shoe 32, conductor 58 to the primary of thetransformer 56, conductor 57 to the frame 30 of the car and thence by the wheels and axles to the track rail 1 and by conductor 16 back to the other terminal of the secondary of the transformer 15.

The current flowing in the primary of the transformer 56, being alternating in character, induces a like alternating current in the secondary of said transformer which passes through the relay 52, energizes it and raises its armature 53 to close the pick up circuit Number Three for the control relay 37. In this way, at the same time that circuit NumberTwo which normally maintains the control relay 3'? energized, is broken by raising the shoe 32', another circuit Number Three for energizing said control relay 3'? established; and consequently the armaturcs 88 and 39 of said control relay are maintained in their upper position, and the train control device K remains idle or inactive.

When the'first wheels and axle of the train. pass from the block A and enter the block B, the track relay 10 will be deenergized, as will be clearly understood by those skilled in the art of railway signaling; and the armature 13 of said track relay 10 will drop and interrupt the circuit Number Five which energizes the alternatin current relay52. -Since the block C is med to be unoccupied, the track relay 10 is energized and its armature 14 is in its upper position, so that a low difference of potential will be created between the ramp R and the track will and energize the primary of the transformer 56 and consequently the alternat currc pick up relay according to a circuit which may be traced as follows:

From the low voltage tap 17 of the secondary of the transformer 15 conductor 67 armature 1& of tie track relay 10 in its upper position, conductors 66 and armature 19 of the relay 3 in its closed position, coil 24 of the relay S conductor Lseeata 6i, miniature 13 of the track relay 10 in its lower position, conductor 62, ramp ll, shoe conductor 58, primary of the transformer conductor 57, frame 30 of the car and thence by the wheels and axles to the track rail 1 and by conductor 16 back to the other inal of the secondary of the transer 15 alternating current pick up relay 52 is So designed that, when its armature 53 is in its upper position, the current induced in the secondary or the transformer 56, when the low difierence of potential is applied to its primary according to circuit N umber Six, is suflicient to hold the armature 53 in upper position; but such current is not sufiicient to cause said armature 53 to be raised from its lower position. In other words, it is necessary to apply high voltage to the primary of the transformer 56 in order to cause the relay 52 to raise its armature 53 from its lower position; whereas a low voltage across the primary of the transformer 56 is suflicient to maintain the armature 5 in its "aised position. This characteristic of the relay may be obtained in a number of different ways, as will be readily appreciated bythose skilled in the art; and, consequently, a detail description of a suitable construction for the relay 52 is deemed to be unnecessary.

From the foregoing it can be seen tha when neither of the blocks B nor Q are occupied by a train, and a train passes from the l into the block 13, the control relay 'u nergized, will be reenergized, or if energy ed, will remain energized; and conse quentl -J train control device K is not set into operation.

For the next condition of traflic to be considered, assume that a train is in the block -r and is about to enter block B; that this train has found the trackway unobstructed and has been travelin unrestrictec by the train control device In; and that, while the block B is not occupied by a train, a train couples the block C. Under these conditions, as the train approaches the ramp R .ts firstshoe 32 engages said ramp, a high 5 erence of potential will exist between the ramp and the track rail 1 according to the circuit Number F our hereinbefore set tr th; and, consequently, the control relay I, will remain energized. When the first wheels and axle of the train pass from the block A into the block 13, the track relay 10 is; deenergized and there will be no difference of potential between the ramp ll and the track rail 1, since it is assumed that a train occupies the block C and causes the track relay 10 to be deenergized and its armaturell to drop and interrupt the circuit Number Six hereinbefore set forth. Since the rais ing of the shoe 32- broke the circuit Number Two which normally holds the control relay 37 energized, and since there is no difference 'of potential between the ramp R and the track rail 1, such as would energize the alternatmg current pick up'relay 52 so as to close the other circuith umber Three for energizing the control relay 37, said control relay 37 is totally deenergized and its armatures 38' and 39 will drop. WVhen thearmature 38 of the control relay 37 drops, it opens a break in the circuit Number Two which normally"energizes the control relay 37, so that after the shoe 32 has left contact with the ramp R and said circuit Number Two is closed at the shoe, nevertheless, said circuit Number Two will not be reestablished. When the armature 39 of the'control relay 37 drops, it breaksthe circuit Number One which normally energizes the control device K; and

, scription of the operation of the parts of consequently, said control device K is set into operation to control the train.

From the foregoing it can be seen that when the block C is occupied by a train and a following train enters the block B, the control device K on the following train will be set into operation. With this general dethe system,which description of the operation will be found fully amplified in said application, Serial No. 38,132 hereinbefore mentioned, the particular arrangement of devices and circuits, with which this invention deals more particularly, can be pointed out. a I Assume that the train includes two or more motor cars or locomotives,'each of which is provided with a contact shoe 32, a control relay 37, an alternating current relay 52, and the associated electrical devices and connections, said devices being electrically connected by the continuous conductor or bus- 59; and further assume that said train is long enough to "span the distance between two successlve rampsso that the contact shoe 4 of two different motor cars or locomotives are in contact with the two rampsat the same time. Disregarding for the moment the operation of the relays S and'assuming that their armatures 19'are in their closed posltlon, with the condition such as assumed,

it can be seen that there is established a path 'of comparative low resistance including part of the secondary of the transformer 15 said path being as follows:

Circuit Number Seven. Commencing at the high voltagetap 18 I of the secondary of the transformer 15 conductor 63 armature 13 of the track relay 10 in its upper position, conductor 62, ramp R shoe 32 'of the front car, conductors-58 59,and 58, the shoe 32 of the rear 7 car, ramp R, conductor 62, armature 13 of the track relay 10 in its lower position, conductor 64c, coil 24: of. the relay S armature 19 of the relay S inits closed position, conary of the transformer 15 'ductors 65 and 66 armature 14: of the track relay 10 in its upper position and conductor 67 to the low voltage tap 17 of the second- There is also established another conducting path for current to flow which includes the other part of the secondary of thetransformer 15 said path being the same as the circuit hereinbefore described and designated circuit N umber Six. Also, there is established a conducting path along which current may flow winch includes both parts of the secondary of the transformer 15 said ath bein analo 'ous to the circuit herein- ,before described and designated circuit Number Five, this path for the ramp R being as follows:

Circuit Number Eight.

From the high voltage tap 18 of the secondary of the transformer 15 conductor 63 armature 13 of the track relay 10 in its upper position, conductor 62 ramp R front contact shoe 32, conductor 58, primary of the transformer 56, conductor 57 to the frame 30 of the front car and thence bythe wheels and axles tothe track rail 1 and by conductor 16 back to the other terminal of the secondary of the transformer 15.

It should be noted that the low voltage tap 17 and the high voltage tap 18 are of the same polarity at any given instant, and i for convenience it will be assumed that these positive, as marked on the these circuits, which are both established under the particular conditions assumed,

have parts in common, namely, the conduc tor 67 the armature 14 conductors 66 65 'armature,19 coil 2%, conductor 64, armature l3, conductor 62, shoe 32 and conductor 58; At the point where the conductor 58 connects wlth the primary of the trans former 56 these two circuits Numbers Six and Seven divide, the circuit Number Six passing through the primaries of the different transformers on the several cars of the train, while circuit Number Seven passes along the bus 59, conductor 58 to the ramp R and thence to the high voltage 18 of the transformer 15 In fact, the circuits NumbQlS'SlX and Seven are arranged according to the well known three-wire system of distribution, the parts including conductor 67 and so forth, which are common to these two circuits being in effect the neutral wire of this three-wire system; and, as is well known, current will" flow in this neutral wire tap 17 and the voltage between the low.

voltage tap 17 and the high voltage tap 18 It can be seen that the parts oi circuit Number Seven which are peculiar to it namely,

conductors 63 62 58 and 59, are compara tively low resistance conductors; whereas the parts of circuit Number Six whichare peculiar to it include the primaries of the transformers 56 on the several motor cars or locomotives of the train. Consequently, the flow of current in the two circuits Numbers Six and Seven is not balanced and with the voltages and resistances which are considered to be best adapted for practical operation, it is found that a relatively large current flows in the conducting path from the ramp Rthrough the coilZi of the relay '21 to the low voltage tap 17 in the direction indicated by the arrow Z). In other words, it may be said that a part of the secondary of the transformer 15 between the tap 17 and the tap 18 is practically short circuited; and this short circuiting not only causes an improper and excessive current to flow through said secondary and the other parts ofthe circuit, but also prevents the proper energization ofthe pick up alternating current relays 52 by circuit Number Eight, even though traiiic conditions are such that said relays should be energized. The relays 52 are not properly energized under the particular conditions assumed for the reason that instead of a large current derived from the high voltage sourceflowing through the primaries of the transformers 56 on the several cars of the train, the current flowing through the primaries of said transformers is practically all derived from the low voltage source only and is too small to pick up the relays 52.

-For these reasons, the above described short circuit should be avoided in order to save the wiring and apparatus from injury by the excessive current flowing and also to prevent unnecessary delay to'the train by .a failure to restore the train control apparatus .to its normal condition, although it is proper to do so.

cuit of part oi the secondary of the transformer 15 the action of the relay S was disregarded; but it can be seen that under the conditions assumed current flowing through the coil 24 of the relay S1 in the direction indicated by the arrow 6. As pointed out hereinbefore, the relay S is of the type commonly known as a polyphase relay; and one characteristic of this type of relay, which is well knownto those skilled In the above discussion of the short cirin the art of railway signaling, is that the rotor or armature actuating member of said relay may be caused to turn in one direction nary and normal conditions, when a train first enters the block 13, current flows in the circuitlluniher Six from the low voltage tap 17 of the secondary of the transformer 15 the ramp 153 through the coil 24: of the relay S in the direction indicated by the arrow (4. Inshort, normal and proper current flows through the coil 24 in the direction indicated by the arrow a, whereas the improper and excessive current flows in the direction indicated by the arrow 6. The

relay S is so designed that when the proper current flows through its coil 2& in the direction indicated by the arrow a, the Phase relation between that current and the current in the coil 20 of said relay is-such as to cause the armature 19 of said relay to close and remain in its closed position. On the other hand, when the excessive-and improper current flows through the coil 24 of the relay S the phase relation of that current and the current flowing in the coil 20 of said reny is such as to move the armature 19 to its open position. When the armature19 is opened, the normally closed low resistance shunt around the impedance 25 is interrupted, so that all of the excessive current flowing along conductor 66 must pass through the coil 2& along conductor 69 through the impedance 25 and along conductor 68 in order to reach the conductor (it. The impedance 25 is so proportioned according to the voltage between the taps 17 and 18 of the secondary of the transformer 15 and according to the resistances and impedances of the other parts of the circuits Numbers Six and Seven that said impedance 25 will limit the flow of improper current to an amount small enough not to do an damage and yet large enough to maintain the coil 2& of the relay S energized. If desired the impedance 25 instead of being a separate impedance external to the winding of the relay S may be made a part of the winding of saidrela-y; and when the impedance 25 is so made a part of the. winding of the relay S it assists in holding the armature 19 open and also has its impedance materially increased by reason of this location.

From a consideration of the circuits shown and hereinbefore traced it can be seen that, in effect, there are two partial circuits associated with each ramp, one of said partial circuits including the entire secondary of the transformer 15 associated with that further that the current limiting impedance 25 and the relay S are included in said sec- 'ond mentioned partial circuit.

The parts of the automatic train control system :shown and described are arranged and designed to'be operated by alternating current, but it is to be understood that by a simple modification, which will be apparent V to those skilled in the art of railway signalcontrolling of my'invention, and explained the operation and principle thereof; nevertheless, I desire to have it understoodthat the form selected is merely illustrative, but does not exhaust the possible physical embodiments of the idea of means underlying my inven tion.

} WVhat I claim as new and desire tosecure by Letters Patent of the United States, is:

1. In an automatic train control system, in combination: insulated contact rails located along the trackway for said trains; a

source of current associated with each contact rail; a partial circuit includ ng said source of current, said contact rall and a track rail'of said trackway; current limi ing means; and means interposed in said partial circuit and responsive to a predetermined direction of flow of current therein for connecting said current limiting means into said partial circuit.

"2. In an automatic train control system,

in combination: insulated contact rails 10- cated along the trackway for said trains; a

source of current associated with each of said contact rails; a partlal circuit includlng said source of current, said contact rail and a track rail of said trackway; current limit ing means interposed in said partial circuit; a normally closed shunt for. said current limiting means; and means interposed in said partial circuit andresponsive to a predetermined direction of flow in current therein for opening said shunt.

3. In an automatic train control system, in combination; insulated contact rails lovtted at intervals along the trackway for said trains; two sources of current connected in series and associated with each contact rail; a partial circuit including both or" said sources, the corresponding contact rail and rails of.

a track rail of the trackway; a second partial circuit including one of said sources of current the preceding contact rail and a t 'ack rail of the trackway; current limiting means; and a polarized translating device interposed in said second partial circuit and operated by a flow of current therein in a predetermined direction for, connecting said current limiting means into said second partial circuit.

4. In an autonmtic train control system, in combinationa traclrway divided "ito electrically isoia ed blocks; an insulated ramp located at the entrance of each of said blocks; a source of current and a track relay associates with each block and forming with the track ra" of that block a normally ciosed track circuit; separate sources of current associated with each ramp; a partial circuit associated with each ramp and closed when the track relay of the block protected by that ramp is energized for connecting one of said sources of current across the trackway and said ramp;'a second partial'cir cuit associatedv with each ramp and closed when the track relay ot'the block protected by that ramp is energized and the track relay of the preceding block is deenergized; said second partial circuit connecting the other source of current across the track rails and the preceding ramp; current limiting means; and means operated by a flow of current in said second partial circuit in a certain direction for interposing said currentlimiting means'in said second partial circuit.

5. In an automatic train control system, in combination: an insulated ramp; a partial circuit for establishing a'diiierence of potential between said ramp and the track the trackway for the trains; and current limiting means operable upon the iiowbf current in one direction interposed in said partial circuit.

6. In an automatic train control system, in combination with a train including a iuun'ber of vehicles each having a contact shoe, said contact shoes being electrically Y connected together, of automatic train control apparatus on each, vehicl controlled by a partial circuit terminating at the corresponding contact shoe and the wheels of the vehicle, contact rails located at intervals along the track, two sources of current connected in series and associated with each contact rail, a partial circuit including both of said sources, the corresponding contact rail and a track rail, a second partial circuit including one of said sources, the con tact rail next in the rear and a track rail, and current limiting means operable upon a flow of current in a certain direction in said second partial circuit and interposed in said second partial circuit.

'7. In an automatic train control system,

Cir

in combination with a track divided into track circuit blocks, a contact rail located adjacent to the entrance end of each block, a partial circuit including a source of current and terminating at the contact rails of two succe sive blocks, said partial circuit being established when a train occupies the block between these contact rails, and means included in said partial circuit and operable upon the fiow oi? current therein for limiting the flow of current in said partial circuit.

8. In an automatic train control system, in combination with a track divided into track circuit blocks each having a track relay, a' contact rail associated with each block, a partial circuit for each contact rail terminating at that contact rail and a track rail, said partial circuit including a source of current, a back contact in the track relay of the corresponding block and a front contact of the track relay of the second block in advance, and means operatively responsive to the polarity of the current flowing in said partial circuit for limiting the flow of current therein.

9. In an automatic train control system, in combination with impulse transmltting means located at intervals along the track, a circuit, including a source of current and established under safe trafiic conditions for governing each impulse transmitting means, andrmeans includedin said circuit and acting automatically upon a flow of certain current therein for obstructing such flow of current, said means being unaffected by current flowing in said circuit from said source.

10. In an automatic system for protecting railway tratlic, the combination with a contact rail located adjacent to the railroad track and insulated therefrom, of a partial circuit including a source of current and ticular flow of current in said circuit for controlling said shunt.

11. In an automatic system for protecting traffic on railroads, the comblnation with a contact rail located ad acent to the railroad track and insulated therefrom, of partial circuit including a source of alternating current and termniating at said contact rail and a track rail, an impedance included in said circuit, a normally closed shunt-tor said impedance, and electromagnetic means acting automatically upon a flow of current of a predetermined character in said circuit for opening said shunt.

12. In an automatic system for protecting trailic on railroads, the combination with a train including a number of vehicles each having a contact shoe, a conductor electri cally connecting the contact shoes of the train, automatic train control apparatus on each vehicle connected between said conductor and the frame of the vehicle, contact rails located at intervals along the track and having their electrical conditions dependent on traffic conditions in advance thereof, and means along the track for automatically limiting the flow of current from one contact shoe to another contact shoe on the train.

13. In an automatic train control system, a trackway impulse device, a circuit ror energizing said device, and current limiting means in said circuit operable automatically upon the flow of current in a predetermined direction therein.

1%. In an automatic train control system for railroads having tracks divided into blocks each provided with a track circuit, an impulse device on the track near the entrance to each block, a circuit for energizing each device governed by the track circuit oi? the block next in advance, and current limiting means for said circuit operable automatically by a predetermined flow of current therein.

15. In an automatic train control system, a traclnvay impulse device, a circuit including a source of alternating current for enen gizing said device, an impedance, circuit controlling means adapted to include said impedance in said circuit, and a polyphase relay for operating said means.

WINTHROP K. HOWE 

